1. Field of the Invention
This invention relates to compositions useful as thermosetting powder coatings. These compositions are used as insulative coatings on electrical conductors such as aluminum and copper magnet wire (wire for magnetic coils).
2. Description of the Prior Art
Traditionally, magnet wire, i.e. wire employed in magnetic coils, have been electrically insulated with enamel coatings. In the conventional wire enamelling process single strands of cleaned and annealed copper or aluminum wire of round or rectangular cross section are passed, horizontally or vertically, through a trough containing circulated and continuously filtered enamel. Excess enamel is removed from the wire and the thus-coated wire is passed through an oven in which the enamel solvent is evaporated and the resin formulation is allowed to flow out, level and cure. This process may have to be repeated several times in order to produce a coating of the desired thickness without pinholes, blistering, sagging or bubble entrapment.
While the enamelling process can produce satisfactory coatings, it has several significant drawbacks. For example, the enamel contains a relatively large amount of organic solvent, which is evaporated in the curing oven. This results in pollution problems which can generally be cured only by the use of expensive solvent recovery equipment. The need to remove the solvent from the enamel coating also causes potential problems in the film properties of the coating. If the solvent is removed too rapidly, blistering or bubble entrapment can occur.
For the above reasons, it is highly desirable to employ solvent-free wire coatings. One alternative to the solvent-containing enamel coatings has been electrostatic powder coatings. However, while electrostatic powder coatings can be used to overcome many of the drawbacks of the enamelling process they have still not proven entirely satisfactory. One problem which still exists is the entrapment of air in the cured coating, resulting in a potential decrease in the dielectric strength of the coating.